1. Field of the Invention
This invention relates in general to systems that process and transmit data and more particularly, to such systems that rely on sequence number tracking to perform such processing and transmission.
2. Description of the Related Art
Many wireless carriers now wish to install communications networks that can handle high-speed, packet data services. As an example, to target these wireless carriers, Motorola, Inc. of Schaumburg, Ill. has developed Wideband Integrated Digital Enhanced Network, or WiDEN. Typically, WIDEN can include up to four communications channels or carriers to transport data between a communications network and a mobile unit. As an example, an outbound reservation—a sequence of time slots containing data intended for a particular mobile unit—may be transmitted to the mobile unit from the network over the four carriers.
Generally, one of these time slots will include a header and the following time slots will contain extension blocks, which can carry data that is meant to be processed by the mobile unit. Each of these extension blocks may be assigned a sequence number, which increases by one for every extension block. For example, when the mobile unit receives a header, the mobile unit can initialize the extension block sequence number (EBSN) to zero and can increment by one the value of the EBSN each time that the mobile unit receives an extension block. The EBSNs can permit the mobile unit to verify that it has received the incoming data in a proper order.
To save bandwidth, the extension blocks are implicitly numbered with the EBSNs, which means that the EBSNs are incorporated into an error detection algorithm, such as cyclic redundancy code (CRC). As such, the mobile unit can verify the correct EBSN by performing a CRC calculation using the mobile unit's internal copy of the EBSN. Unfortunately, if one or more of the carriers fail for any particular reason, the CRC computation will fail, and the mobile unit will discard the data. That is, if the EBSN internal to the mobile unit becomes unsynchronized with the EBSN provided by the network, the mobile unit will not accept the transmitted data. In addition, the mobile unit will request that the network resend the sequence of time slots, beginning with the extension block where the carrier failure occurred. This process reduces the processing performance of the mobile unit, wastes valuable bandwidth and negatively affects battery life, particularly if the failure occurs at an extension block that is near the header.